1. Field of the Invention
The present invention relates to a thermionic electron emission device adopting carbon nanotubes and a method for making the same.
2. Discussion of Related Art
Carbon nanotubes (CNT) are a carbonaceous material and have received much interest since the early 1990s. Carbon nanotubes have interesting and potentially useful electrical and mechanical properties. Due to these and other properties, CNTs have become a significant contributor to the research and development of electron emitting devices, sensors, and transistors, among other devices.
Generally, there are two kinds of electron-emitting devices; field emission device and thermionic electron emission device. The field emission device includes an insulating substrate, and a plurality of grids located thereon. Each grid includes first, second, third and fourth electrode down-leads located on the periphery of the gird. The first and the second electrode down-leads are parallel to each other. The third and fourth electrode down-leads are parallel to each other. The first and the second electrode down-leads are insulated from the third and fourth electrode down-leads.
The thermionic electron emission device, conventionally, comprises a plurality of thermionic electron emission units. Each thermionic electron emission unit includes a thermionic electron emitter and two electrodes. The thermionic electron emitter is located between the two electrodes and electrically connected thereto. The thermionic emitter is generally made of a metal, a boride or an alkaline earth metal carbonate. The thermionic emitter, made of metal, can be a metal ribbon or a metal thread, and is fixed between the two electrodes by welding. The boride or alkaline earth metal carbonate can be dispersed in conductive slurry, wherein the conductive slurry is directly coated or sprayed on a heater. The heater can be secured between the two electrodes as a thermionic electron emitter. However, it is hard to assemble a plurality of thermionic electron emission units, and the assembled thermionic electron emission device cannot realize uniform thermionic emission. Further, the size of the thermionic emitter using the metal, boride or alkaline earth metal carbonate is large, and thereby limits its application in micro-devices. Furthermore, the coating formed by direct coating or from spraying the metal, boride or alkaline earth metal carbonate has a high resistivity, and thus, the thermionic electron source using the same has greater power consumption and is therefore not suitable for applications involving high current density and brightness.
What is needed, therefore, is a thermionic electron emission device and a method for making the same, wherein the thermionic electron emission device has excellent thermal electron emitting properties, and can be used in flat panel displays with high current density and brightness, logic circuits, as well as in other fields using thermionic electron emission devices.